TABLE OF CONTENTS ~ COMMENTARY ON PRELIMINARY DESIGN · PDF fileTABLE OF CONTENTS ~ COMMENTARY...

IOWA DOT ~ OFFICE OF BRIDGES AND STRUCTURES ~ LRFD BRIDGE DESIGN MANUAL COMMENTARY ~ C3: 1

January 2018

TABLE OF CONTENTS ~ COMMENTARY ON PRELIMINARY DESIGN OF BRIDGES

C3 Preliminary C3.1 General

C3.1.1 Policy overview C3.1.2 Design information C3.1.3 Definitions C3.1.4 Abbreviations and notation C3.1.5 References

C3.1.5.1 Direct C3.1.5.2 Indirect

C3.2 Bridges C3.2.1 Identification numbers C3.2.2 Stream and river crossings

C3.2.2.1 Hydrology C3.2.2.2 Hydraulics C3.2.2.3 Backwater C3.2.2.4 Freeboard C3.2.2.5 Road grade overflow C3.2.2.6 Streambank protection C3.2.2.7 Scour

C3.2.2.7.1 Types C3.2.2.7.2 Design conditions C3.2.2.7.3 Evaluating existing structures C3.2.2.7.4 Depth estimates C3.2.2.7.5 Countermeasures C3.2.2.7.5.1 Riprap at abutments C3.2.2.7.5.2 Riprap at piers C3.2.2.7.5.3 Wing dikes C3.2.2.7.6 Coding

C3.3 Highway crossings C3.3.1 Clearances C3.3.2 Ditch drainage

C3.4 Railroad crossings C3.4.1 BNSF and UP overhead structures

C3.4.1.1 Vertical clearance C3.4.1.2 Horizontal clearance C3.4.1.3 Piers C3.4.1.4 Bridge berms C3.4.1.5 Drainage C3.4.1.6 Barrier rails and fencing

C3.4.2 Non-BNSF and -UP overhead structures C3.4.2.1 Vertical clearance C3.4.2.2 Horizontal clearance C3.4.2.3 Piers C3.4.2.4 Bridge berms C3.4.2.5 Drainage C3.4.2.6 Barrier rails and fencing

C3.4.3 Underpass structures C3.4.4 Submittals

C3.5 Pedestrian and shared use path crossings C3.6 Superstructures

C3.6.1 Type and span C3.6.1.1 CCS J-series C3.6.1.2 Single-span PPCB HSI-series C3.6.1.3 Two-span BT-series


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C3.6.1.4 Three-span PPCB H-series C3.6.1.5 Three-span RSB-series C3.6.1.6 PPCB C3.6.1.7 CWPG C3.6.1.8 Cable/Arch/Truss

C3.6.2 Width C3.6.2.1 Highway C3.6.2.2 Sidewalk, separated path, and bicycle lane

C3.6.3 Horizontal curve C3.6.3.1 Spiral curve

C3.6.4 Alignment and profile grade C3.6.5 Cross slope drainage C3.6.6 Deck drainage C3.6.7 Bridge inspection/maintenance accessibility C3.6.8 Barrier rails C3.6.9 Staging

C3.7 Substructures C3.7.1 Skew C3.7.2 Abutments C3.7.3 Berms

C3.7.3.1 Slope C3.7.3.2 Toe offset C3.7.3.3 Berm slope location table C3.7.3.4 Recoverable berm location table C3.7.3.5 Slope protection C3.7.3.6 Grading control points C3.7.3.7 Mechanically Stabilized Earth (MSE) Walls adjacent to abutments

C3.7.4 Piers and pier footings C3.7.5 Wing walls

C3.8 Cost estimates C3.9 Type, Size, and Location (TS&L) plans C3.10 Permits and approvals

C3.10.1 Waterway C3.10.2 Railroad C3.10.3 Highway

C3.11 Forms C3.12 Noise walls C3.13 Submittals C3.14 Zone of Intrusion


January 2018

C3 Preliminary

C3.1 General

C3.1.1 Policy overview

C3.1.2 Design information

C3.1.3 Definitions

C3.1.4 Abbreviations and notation

C3.1.5 References

C3.1.5.1 Direct

C3.1.5.2 Indirect

C3.2 Bridges

C3.2.1 Identification numbers

C3.2.2 Stream and river crossings

C3.2.2.1 Hydrology


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January 2018

C3.2.2.2 Hydraulics

C3.2.2.3 Backwater

C3.2.2.4 Freeboard

C3.2.2.5 Road grade overflow

C3.2.2.6 Streambank protection

Bank Toe Protection Example

C3.2.2.7 Scour

Introduction

The most common cause of bridge failures in the nation is flooding, with bridge scour being the most common type

of flood damage. Bridge scour is a complicated process and provides challenges to engineering analysis. Because of

public safety and high replacement and repair costs, the need exists to evaluate or improve current design and

maintenance practices concerning bridge foundations.

The objective in this document is to detail three items:

1. Factors that affect scour.

2. Recommendations to reduce or prevent scour effects on existing and proposed bridges.

3. Methods to estimate scour for existing and proposed structures.


January 2018

Definition

A basic definition of scour is the result of erosive action of moving water as it excavates and carries away material

from a streambed and banks. There are two types of scour:

1. General scour - the loss of material from most or all the bed and banks, usually caused by the road

embankment encroaching onto the flood plain with resulting contraction of the flood flow (often called

contraction scour).

2. Local scour – the loss of material around piers, abutments, spur dikes and embankments.

There are two conditions for contraction and local scour: clear-water and live-bed. Clear-water scour occurs when

there is little to no movement of the bed material of the stream upstream of the crossing. Typical situations include

most overflow bridges, coarse bed material streams, and flat gradient streams during low flow. Live-bed scour

occurs when velocities are high enough to move the bed material upstream of the crossing. Most Iowa streams and

rivers experience live-bed scour.

Streambed degradation, such as in the Western Iowa loess region, is considered in some documents to be scour.

Even though degradation can affect structural stability like local or general scour does, the causes of degradation are

of a different nature, and it will not be discussed in detail in this document.

The effects of scour are a complex problem involving geotechnical, hydraulic, and structural concerns, so decisions

concerning scour should involve engineers in each of these disciplines.

Design guidelines and considerations

Numerous factors affect the stability of the bed and banks of a stream and are discussed below with some guidelines

and considerations.

1. Soils

Soils with any combination of sand or silt have greater potential for scour: sand, silt, sandy silt, sandy silty clay, etc.

As a general rule, according to IDOT's Soils Design Section, soils which have a blow count of ten or less are

particularly susceptible.

Excessive loss of pile bearing due to scour is one cause for bridge damage or failure. However, perhaps a more

common cause of failure is soil instability associated with the road embankment and bridge berm. Often a bridge

berm or fill behind a high abutment has minimal factor of safety for stability. If this safety factor is reduced due to

scour at the toe of the embankment, the soil may become unstable resulting in a slip failure. Damage to an abutment,

pier or approach fill is a possible outcome.

For replacement structures, designing flatter berm slopes and/or placing the abutments farther from the channel will

provide a greater safety factor. Then, when scour does occur, the embankment will more likely remain stable. For

existing structures, protection of the berm, especially the toe, may be necessary.


January 2018

2. Substructure

Generally, wider and longer piers have greater scour potential. Deeper footings and longer piles are more stable at

greater scour depths. Spread footings should be used only on material highly resistant to scour such as limestone

and some shales.

To maintain the integrity of the structure, do not allow scour to reduce pile bearing below a desirable safety factor

that is selected by the structural or geotechnical engineer. Designing for this minimum safety factor may require

designing longer piles for new bridges. For existing structures, protection of the piles may be necessary to maintain

the safety factor.

New bridges should have sufficient length so that the abutments do not encroach on the channel but placed as far

back from the streambank as practical. Vertical wall abutments (high abutments) have a greater potential for general

and local scour as compared to the spill-through type (integral or stub abutments).

3. Flood discharge

In the publication “Evaluating Scour at Bridges, Fifth Edition”, Hydraulic Engineering Circular No. 18 (HEC-18),

the FHWA recommends using scour flood frequencies that are larger than the hydraulic design flood frequencies.

The rationale for this is that hydraulic design involves backwater and ensures that the bridge size will be adequate

under normal flood conditions. In scour design, a higher discharge is used to ensure that the bridge will remain

stable and will not fail or suffer severe damage during extreme flood events. Also, there is a reasonably high

likelihood that the hydraulic design flood will be exceeded during the service life of the bridge.

Iowa DOT recommends using the Q200or lesser discharge for scour analysis, depending on which results in the most

severe scour conditions. Usually the overtopping flood results in the worst scour, so check this flood (if less than

the Q200) and the Q200.

FHWA also recommends checking scour conditions for a superflood, such as a Q500. If Q500 data is not available,

HEC-18 recommends using 1.7 X Q100. The safety factors for the bridge should remain above 1.0 under this flood

condition. Similar to that mentioned above, Qovertopping may be the worst-case flood and should be used if it is less

than Q500.

4. Interaction between road and flood plain

A highly skewed river crossing provides a less hydraulically efficient bridge opening and therefore has a greater

contraction scour potential. Also, a high ratio of overbank flow to main channel flow will result in a greater

contraction scour potential. For these situations, scour can be reduced by using wing dikes and/or riprap.

Road grade overflow or overflow structures may provide relief and reduce scour potential for the main channel

bridge.

5. Interaction between piers and flood flow

The width, length and type of pier (e.g., pile bents, “tee” piers) all have an effect on local scour. Closely spaced piles

in a pile bent pier can act similar to a solid wall. The angle of attack of flood flow to the pier can also significantly

increase scour if this angle changes due to channel meandering during the life of the bridge. For example, if the

angle of attack changes from 0 to 15, the pier scour approximately doubles. The stream’s history of and future

potential for meandering should be examined.


January 2018

6. Debris and ice

Visual observation can be made and maintenance records can be checked to determine the history of debris and ice

on the stream. Debris and ice can snag on the piers or superstructure, placing additional stresses on the bridge as

well as promoting local scour. This scour can sometimes be quite significant although difficult to estimate.

Therefore, for new designs, give consideration to raising the low superstructure above the low road grade elevation.

This will allow hydraulic relief if the bridge opening becomes clogged.

Estimating scour

Procedures for estimating scour have been researched in the past 40 years in an attempt to develop reliable

prediction equations. Some of these equations give reliable results, others do not. The Federal Highway

Administration has attempted to find the best equations and published them in HEC-18.

HEC-18 contains equations for contraction scour, abutment scour and pier scour. The contraction scour equations

are the best available equations of their type and sometimes provide reliable estimates, although these estimates still

need to be evaluated considering soil types, site scour history, etc. The abutment scour equations frequently give

questionable estimates. Because of comments similar to this from various states, FHWA is conducting additional

research to develop new methods. At this time, IDOT recommends not using FHWA's abutment scour equations or,

at most, use them with caution. However, be aware that abutment scour can occur.

Concerning pier scour, the equation in HEC-18 generally gives reliable results. However, a much simpler method

that gives very similar results is found in Iowa Highway Research Board's Bulletin No. 4, “Scour Around Bridge

Piers and Abutments,” by Emmett M. Laursen and Arthur Toch, May 1956. This method for estimating pier scour

can be used in most cases instead of the methods in HEC-18.

1. Contraction scour estimation

See Chapter 4 of HEC-18 for detailed instructions on how to calculate contraction scour. To help explain this

chapter, there are two determinations that must be made when estimating contraction scour:

• The appropriate case of contraction scour that depends on the flow interaction of the bridge to the channel and

floodplain. There are four of these cases. See the figures later in this document for graphical illustrations of

these cases.

• The appropriate sediment transport condition. There are two of these conditions and equations (live-bed and

clear-water) that can occur in any of the four cases mentioned above.

Both determinations are explained below.

Four cases of contraction scour

Case 1 is overbank flow being forced back into the main channel due to the road fill. The majority of bridges in

Iowa will be Case 1. There are three variations to Case 1, depending on the location of the abutments or abutment

berms compared to the channel:

Case 1a is normally used when the river channel width becomes narrower due to the bridge abutments (or

berms) projecting into the channel.

Case 1b does not involve any contraction of the channel itself, but the overbank flow area is completely

obstructed by the embankment. In other words, the abutments or abutment berms are on the channel bank.

Case 1c is when the abutments or abutment berms are set back from the channel. This case is more complex

because there is both main channel flow and overbank flow in the bridge opening. Therefore, refer to

discussion in Section 4.3.4 of HEC-18. More hydraulic analysis may be needed than in Cases 1a and 1b (such

as WSPRO) to determine the distribution of flow in the bridge opening, i.e., what is the discharge in the main

channel (Q2) and the discharge in the overbank under the bridge (Qoverbank2).


January 2018

)(D y 10.95 = V 500.33 0.167

c

W

W

Q

Q =

y

y

2

1

1k

1

2

0.86

1

2

Most Case 1 streams in Iowa will have live-bed scour. However, if the streambed material has particles larger than a

sand classification, calculate Vc (see below) to determine if clear-water scour will occur instead of live-bed scour.

Case 2 is when the stream has no overbank flow. This case will be common in Western Iowa streams that are

severely degraded.

Case 3 is an overflow (relief) bridge with no bed material transport, so use the clear-water scour equations.

Hydraulic analysis (e.g., using WSPRO) is needed to determine the flood plain width associated with the relief

opening and to determine the total flow going through the relief bridge.

Case 4 is an overflow (relief) bridge similar to Case 3 except it does have sediment transport (live-bed scour), such

as over a secondary channel on the flood plain of a larger stream. Hydraulically this case is no different than Case 1

except that analysis (e.g., using WSPRO) is needed to determine the flood plain width associated with the relief

opening and the portion of the total flow going through the relief bridge.

Sediment transport conditions: Live-bed scour versus clear-water scour

Before an equation is selected to estimate contraction scour, it is necessary to determine if the flow is transporting

bed material. If it is, the flow will create live-bed scour. If it is not, the flow will create clear-water scour. There are

different scour equations for each of these sediment transport conditions.

Most Iowa stream channels will be live-bed. In other words, the velocities in the channel will be high enough to

cause movement of the soil particles in the streambed. In order to be sure if the channel is live-bed, Chapter 2 in

HEC-18 gives a simple equation to calculate the velocity needed to cause movement of the soil:

where Vc = critical velocity which will transport bed materials of size D50 and smaller, ft/sec.

y = depth of upstream flow, feet

D50 = median diameter of the bed material, feet

If the velocity in the channel is greater than Vc, then the particles will move and the stream will have live-bed scour.

If the velocity in the channel is less than Vc, then the particles will not move and the stream will have clear-water

scour.

Most Iowa streambeds have sand or silt which results in a very low Vc. This means that even a low flood velocity

will move the particles. Therefore, most Iowa streams will have live-bed scour. For example, for a medium sand

with a D50 of 0.0012 feet and a flow depth of 12 feet, Vc is 1.8 ft/sec. Any flood with a channel velocity higher than

this will cause sediment transport and therefore create live-bed scour. Even a medium gravel streambed with D50 of

0.039 feet and depth of 12 feet results in Vc of 5.7 ft/sec. Again, most Iowa streams will have a channel velocity

higher than this.

In summary, as a rule of thumb, if the streambed material is larger than sand, calculate Vc and compare to expected

channel velocities to determine if live-bed or clear-water scour occurs. If the material is sand or smaller, assume

live-bed scour occurs.

Live-bed scour

From HEC-18, the equation for live-bed scour is as follows:

and ys = y2 - y1 = average scour depth, ft

where y1 = average depth in the upstream main channel, ft


January 2018

W

W

Q

Q =

y

y

2

1

0.64

1

2

0.86

1

2

)(W )D( 139

Q = y

22

500.67

20.43

2

y2 = average depth in the contracted section (i.e., in the bridge opening), ft

W1 = top width of water in the upstream main channel, ft

W2 = top width of water in the main channel in the contracted section (i.e., in the bridge opening), ft

Q1 = discharge in the upstream main channel transporting sediment, cfs.

(Q1 does not include upstream overbank flow)

Q2 = discharge in the contracted channel (i.e., bridge opening), cfs

(For Cases 1a and 1b, Q2 may be the total flow going through the bridge opening. For Case 1c, Q2 is

not the total flow through the bridge since there is also some overbank Q adjacent to the channel

under the bridge.)

k1 = exponent. Assume k1 = 0.64 to simplify the calculations since the range for k1 in HEC-18 Section

4.3.4 makes very little difference on calculated scour depths.

This results in the live-bed scour equation of:

Simply stated, the ratio W1/W2 reflects contraction or expansion in the channel. The ratio Q2/Q1 reflects the effect of

forcing overbank flow through the bridge opening.

This equation is generally used for Case 1 (when streambed consists of sand-size particles or smaller) and Cases 2

and 4. In Case 1c, the live-bed scour equation is used for the main channel contraction scour and the clear-water

scour equation is used for the contraction scour near the abutment on the overbank.

Clear-water scour

From HEC-18, the equation for clear-water scour is as follows:

and ys = y2 - y1 = average scour depth, feet

where y2 = depth in the bridge opening, ft

Q = discharge through the bridge opening or on the overbank portion of the bridge opening, cfs

D50= median diameter of material in overbank, feet (see attached sediment size table from HEC-20)

W2= top width of water in bridge opening or overbank width in bridge opening (set-back distance),

feet

y1 = upstream depth, ft

The average depths y1 and y2 are measured either in the channel for channel scour calculations or on the overbank

for overbank/abutment-area scour calculations.

The clear-water scour equation is used for a few Case 1 bridges (when streambed particles are larger and, in Case

1c, when the abutment is set back a distance from the channel) and for all Case 3 bridges.

Summary of estimating contraction scour

• Determine which “case” is appropriate

• Determine if the channel has live-bed or clear-water scour

• Analyze the hydraulics

• Using the correct equation, estimate scour

• Evaluate the reasonableness of estimated scour


January 2018

2. Abutment scour estimation

The equation given in Section 4.3.6 of HEC-18 is for the worst-case conditions. The equation will predict the

maximum scour that could occur for an abutment projecting into a stream with velocities and depths upstream of the

abutment similar to those in the main channel. In most cases, the equation will over-predict scour, especially the

farther the abutment is from the channel. Do not calculate abutment scour at this time due to this questionable

equation. Be aware, however, that scour at the abutments can occur. Site experience is very important in the

engineering analysis, including known scour occurrences and settlement of approach pavement which indicates soil

stability problems. It is important to note that high abutments may have up to twice the scour depths as spill-through

abutments.

A conservative approach in determining effects of scour on the abutments is to assume that contraction scour is

added to abutment scour when the abutment is near the channel.

Several questions should be considered for abutment stability. Is the soil scourable? What is the effect on berm

stability? Are flatter berm slopes or a longer bridge needed? What is the effect on pile bearing? Are longer piles

needed? Should riprap or wing dikes be used?

3. Pier scour estimation

Use “Scour Around Bridge Piers and Abutments”, Emmett M. Laursen and Arthur Toch, Iowa Highway Research

Board, Bulletin No. 4, 1956, for most cases.

Figure 39 in Bulletin No. 4 is the basic design curve for pier scour. IDOT determined an equation from this curve:

314.0

p

1

p

s

w

y1.485

w

y'

Equation 1

where

y's , unfactored depth of scour, ft

y1 , unscoured depth of flow, ft

wp , width of pier column, ft

Equation 1 is then substituted into the basic equation, resulting in Equation 2 below:

ys = (K) (y's ) = (K) (wp )

w

y'

p

s

ys = 1.485 (K) (wp)

w

y

p

1

314.0

Equation 2

where ys is depth of scour, ft

K, a pier coefficient (either Ka or Ks),

Ks, coefficient for pier nose shape (see below). Use only if angle of attack = 0.

Ka, coefficient for angle of attack if angle is not zero (see table below).


January 2018

Equation 2 should be used to calculate pier scour.

If angle of attack is zero, use one of the following values for Ks, the coefficient for the shape of the upstream nose of

the pier (adapted from Bulletin No. 4). Use this Ks value in Equation 2 in place of K. These values show that the

better the “rounding” of the pier nose, the lower the pier scour.

Rectangular 1.0

Semicircular 0.9

Elliptic 0.8

If angle of attack is not zero, use the following table adapted from Figure 39 in Bulletin No. 4 to determine Ka. In

this table, L = length of pier, and wp = width of pier. Use this Ka value in Equation 2 in place of K. The values in the

table show that as the angle of attack increases, the pier scour increases dramatically. For example, for a pier L/ wp

of 8, if the angle of attack changes from 0 to 15, the factor Ka changes from 1.0 to 2.0, doubling the calculated pier

scour.

Design Factors (Ka ) for Piers Not Aligned With Flow

L/wp

Angle of Attack

4

6

8

10

12

14

0 1.0 1.0 1.0 1.0 1.0 1.0

5 1.2 1.3 1.3 1.5 1.6 1.6

10 1.4 1.5 1.7 1.9 2.1 2.3

15 1.5 1.8 2.0 2.2 2.5 2.7

20 1.7 2.0 2.3 2.5 2.8 3.0

25 1.8 2.2 2.5 2.8 3.1 3.5

30 1.9 2.4 2.7 3.1 3.4 3.8

35 2.0 2.5 2.9 3.3 3.7 4.0

40 2.1 2.7 3.1 3.6 4.0 4.3

45 2.2 2.8 3.3 3.8 4.2 4.6

See Scour Calculation Sheet to assist in pier scour estimation. Other subjects concerning pier scour discussed in

more detail are found in Section 4.3.5 of HEC-18:

• Pier scour for exposed footings and exposed pile groups under a footing

• Pier footings that are above normal streambed

L

wp

wp

wp

ys

y1

wp


January 2018

• Multiple columns in a pier (e.g., a pile bent pier)

• Pressure flow scour

• Scour from debris

• Width of pier scour holes

Summary of estimating pier scour:

• Analyze hydraulics

• Estimate scour

• Evaluate the reasonableness of the estimated scour

• Add pier scour to contraction scour to obtain total scour

• Determine action steps such as countermeasures or design features of the bridge

Coding for the Structure Inventory and Appraisal (SI&A)

See the attached pages from FHWA’s “Recording and Coding Guide for the Structure Inventory and Appraisal of

the Nation’s Bridges” to determine what rating should be given to each bridge. All countermeasures (SI&A Item

113 coded as "7") should be monitored in future years by bridge inspectors.

Countermeasures: reducing the effects of scour

Generally, a new bridge should be designed to withstand scour without countermeasures, especially when the

countermeasures cannot be easily inspected. For example, riprap protecting a pier in the channel is difficult to

inspect, but a wing dike in the overbank is easily inspected and repaired. Countermeasures will be used most

commonly on existing bridges that are scour critical. See HEC-18, Chapter 7, for an in-depth discussion of when and

how to use countermeasures.

In summary, listed below are common considerations to reduce scour on the bridges. Some items may be relevant

only to existing bridges; others may be relevant only in the design phase of a structure.

• Use longer piles.

• Set the pier or abutment footings lower. However, lengthening piles is generally preferred due to lesser

cost.

• Place riprap around the pier, abutment, berm slope, or spur dike or across the entire streambed. Riprap is an

easy and often inexpensive way to protect a bridge.

• Build abutments as far from the streambank as possible.

• Remove debris from piers.

• Wing dikes (a.k.a., spur dikes, guide banks) provide for a more hydraulically efficient bridge opening and

force the scour to occur on the dike, which is expendable, rather than on the bridge itself.

More expensive solutions can be considered in some instances:

• Place sheet piling to protect existing piers or abutments.

• Underpin the foundation.

• Replace with a new bridge.

• Construct an additional span.

• Overflow (relief) bridges can be used on flood plains that have substantial overbank flow. This provides

relief for the main channel bridge. However, be aware that these overflow structures are particularly

susceptible to deep scour. Twenty to thirty feet of scour is not uncommon.

• Provide for road grade overflow which is a “relief valve” to the bridge opening during extreme flood events

and can prevent or minimize damage to the bridge. A disadvantage to road grade overflow is potential

hazard to the traveling public when water is over the road. These factors need to be weighed by the

engineer when considering other factors such as traffic volumes, traffic speeds and costs.


January 2018

153.6

) V(K = D

2

50

Following are some design guidelines for sizing riprap and placing wing dikes as countermeasures. The

recommendations concerning riprap are not intended to determine if it is needed, rather only how to properly size

riprap.

1. Riprap at abutments.

Section 7.5.1 in HEC-18 gives several equations for sizing riprap at abutments. Considering these equations and past

experience, IDOT recommends simplifying riprap design to the following:

When riprap is needed for countermeasure and the toe of the abutment berm or the vertical abutment is

approximately 75 feet or less from the top of the bank, use the average velocity through the entire bridge opening to

size the riprap. When the toe of the abutment berm or the vertical abutment is approximately 75 feet or more from

the top of the streambank, use the average velocity in the overbank portion of the bridge opening.

When riprap is needed and the determined average velocity is less than approximately 8 feet per second, use IDOT’s

Class E riprap (D50 of 90 pounds). When the determined average velocity is greater than approximately 8 feet per

second, use the Class B gradation which is heavier than Class E (D50 of 275 pounds).

2. Riprap at piers.

From Section 7.5.1 in HEC-18, the equation for sizing riprap at piers reduces to the following (assuming specific

gravity of 2.65 for riprap):

where D50 = median stone diameter, feet

K = coefficient for pier shape (1.5 for round-nose pier, 1.7 for square-nose pier)

V = average velocity approaching pier, ft/sec

To determine V, multiply the average channel velocity (Q/A) by a coefficient that ranges from 0.9 for a pier near the

bank in a straight uniform reach of the stream to 1.7 for a pier in the main current of flow around a bend.

The D50 for IDOT's Class E riprap is 90 pounds or approximately 1.0-foot diameter and will be adequate for many

situations. From the above equation, this diameter will tolerate a velocity of 8.3 ft/sec for round-nose piers and 7.3

ft/sec for square-nose piers.

When the adjusted velocity exceeds this and riprap is needed as a countermeasure, consider using Class B riprap.

This has a D50 of 275 pounds which is approximately 1.5 feet in diameter and will tolerate a velocity of

approximately 10 ft/sec for round-nose piers and 9 ft/sec for square-nose piers. This gradation should be adequate in

almost all situations where the standard gradation is not adequate.

According to HEC-18, the width of the riprap around the pier should at least twice the pier column width. However,

on several countermeasure projects, IDOT has placed a much wider layer (25’) around the entire pier. The riprap

should be placed at or below the streambed so as not to create a greater obstruction to flow. HEC-18 recommends a

thickness for the pier scour protection layer of 3 x D50 or greater. IDOT has used thicknesses of three and four feet

on previous projects. Either guideline seems reasonable.

3. Wing dikes

Use Office of Design’s Standard Road Plan EW-210. See C3.2.2.7.5.3 for a table to determine the length of wing

dikes. See also HEC-20 or HDS No. 1 for further guidance.


January 2018

References

1. “Evaluating Scour at Bridges”, Hydraulic Engineering Circular No. 18, Federal Highway Administration,

Second Edition, April 1993.

2. “Evaluating Scour at Bridges”, Hydraulic Engineering Circular No. 18, Federal Highway Administration, Third

Edition, November 1995.

3. “Scour Around Bridge Piers and Abutments”, Emmett M. Laursen and Arthur Toch, Iowa Highway Research

Board, Bulletin No. 4, May 1956.

4. “Hydraulics of Bridge Waterways”, Hydraulic Design Series No. 1, Federal Highway Administration, March

1978.

5. “Design of Riprap Revetment”, Hydraulic Engineering Circular No. 11, Federal Highway Administration, 1989.

6. “Stream Stability at Highway Structures”, Hydraulic Engineering Circular No. 20, Federal Highway

Administration, February 1991.

7. “Stream Stability at Highway Structures”, Hydraulic Engineering Circular No. 20, Federal Highway

Administration, Second Edition, November 1995.

8. “Recording and Coding Guide for the Structure Inventory and Appraisal of the Nation's Bridges”, Federal

Highway Administration, December 1995.

9. “Evaluating Scour at Bridges”, Hydraulic Engineering Circular No. 18, Federal Highway Administration, Fifth

Edition, April 2012.


January 2018

SCOUR CALCULATION SHEET LOCATION County_________________ Hwy. No.___________Des. No. ________________ Maint. No. _____________ FHWA No.__________ Stream________________ Drain. Area_______sq. mi. Twp______ Range_______ Section_____ Prepared by____________ Date_________________ BRIDGE DESCRIPTION Size and Type______________________________________________________ Pier Type_______________ Width__________ft Shape Coeff (Ks)________ Angle of Attack _____ Coeff (Kal)_______ Pile Type___________ Pile Length below Str.Bed_____ Pile Tip Elev.______ Abutment Type_______________ Pile Type________Pile Length_________ Pile Tip Elev.________ Berm Slope_______(proposed or existing) STREAM INFORMATION Exist. Streambed Elev.______ Stream Slope______ft/mi n-values: LOB__________ Channel_____________ROB________________ Soils: Type __________________ Depth* ________ D50 __________ft

Type __________________ Depth* ________ Type __________________ Depth* ________ Type __________________ Depth* ________ *below streambed

Streambed Degradation At this site _____________________ feet since _______ year At other known sites _____________ feet since _______ year Estimated future degradation _______feet

HYDROLOGIC/ HYDRAULIC INFORMATION Low road elev. ______________ Methodology used to determine: Q _____________ Water surface elev. ___________ Q200 Q500 or Qovertopping Discharge (Q), cfs ____________ _____________ Water surface elev. ____________ _____________ y1, depth in main channel, ft ____________ _____________ Vel. in main channel, fps ____________ _____________


January 2018

W

W

Q

Q =

y

y

2

1

0.64

1

2

0.86

1

2

)W( )(D 139

Q = y

22

500.67

20.43

2

CONTRACTION SCOUR Vc = 10.95 y0.167 D50

0.33 = _______________ ft/sec. If Vc < average channel velocity, use live-bed scour equation. If Vc > average channel velocity, use clear-water scour equation.

Live-bed scour

Generally, used for Cases 1a, 1b, 2, and 4, and also for the main channel scour portion of Case 1c. See Section 4.3.4 in HEC-18.

Q200 Q500 or Qovertopping Q2, discharge in the contracted channel, cfs ____________ ____________ Q1, discharge in the upstream main channel, cfs ____________ ____________ W1, top width of the upstream main channel, ft ____________ ____________ W2, top width of the main channel in contracted section (i.e., bridge opening), ft ____________ ____________ y1, ave. depth in upstream main channel, ft ____________ ____________ y2, ave. depth in contracted section, ft ____________ ____________ ys = y2 - y1 = ave. scour depth, ft ____________ ____________

Clear-water scour

For Case 3 and the overbank area of the bridge opening for Case 1c. Occasionally used for Cases 1a, 1b, 1c (main channel portion), and 2. See Section 4.3.4 in HEC-18.

Q200 Q500 or Qovertopping

y2, depth in bridge opening, ft __________ ____________ Q, discharge through bridge opening or on overbank portion of bridge opening, cfs __________ ____________ D50, median diameter of material in overbank, ft __________ ____________ W2, top width of bridge opening or overbank width in bridge opening, ft __________ ____________ y1, upstream depth, ft __________ ____________ ys = y2 - y1 = ave. scour depth, ft __________ ____________

Is this contraction scour depth realistic? Is the soil scourable? What is the effect on berm stability (including any abutment scour)? Are longer abutment piles or a flatter abutment berm needed? Should riprap or wing dikes be used? Other comments?


January 2018

PIER SCOUR Use “Scour Around Bridge Piers and Abutments”, Emmett M. Laursen and Arthur Toch, Iowa Highway Research Board Bulletin No. 4, 1956, for most cases. Use Equation 2 below and previous discussion in the text. Also, see Section 4.3.5 in HEC-18 for more discussion on estimating pier scour.

ys = 1.485 (K) (wp)

w

y

p

1

314.0

Equation 2

where ys, depth of scour, ft

y1 , unscoured depth of flow, ft wp, width of pier column, ft

K, a pier coefficient (either Ks or Ka), Ks, coefficient for pier nose shape (see values in text). Use only if angle of attack = 0. Ka, coefficient for angle of attack if angle is not zero (see table in text).

Q200 Q500 or Qovertopping y1, ft ______________ _________________ wp, ft ______________ _________________ K (either Ka or Ks) _______________ _________________ ys, ft (from Equation 2) ______________ _________________

TOTAL SCOUR AT PIER = pier scour (ys) + contraction scour (ys)

ys, ft (pier) ______________ _________________ ys, ft (contraction) ______________ _________________ Total scour, ft ______________ _________________ Normal streambed elev. ______________ _________________ Scour elevation ______________ _________________

Is ys or the total scour depth at the pier realistic? Is the soil scourable? What is the effect on pile stability? Should riprap or other countermeasures be used? What is the rating for SI&A Item 113? Other comments?


January 2018

Sediment Grade Scale, from “Stream Stability at Highway Structures”, Hydraulic Engineering Circular No. 20,

Federal Highway Administration, Fourth Edition, April 2012.

SEDIMENT GRADE SCALE

Size Approximate Sieve Mesh

Openings (per inch)

Class

Millimeters Microns Inches Tyler U.S. Standard

4000-2000 --- 180-160 --- --- Very Large Boulders

2000-1000 --- 80-40 --- --- Large Boulders

1000-500 --- 40-20 --- --- Medium Boulders

500-250 --- 20-10 --- --- Small Boulders

250-130 --- 10-5 --- --- Large Cobbles

130-64 --- 5-2.5 --- --- Small Cobbles

64-32 --- 2.5-1.3 --- --- Very Coarse Gravel

32-16 --- 1.3-0.6 --- --- Coarse Gravel

16-8 --- 0.6-0.3 2.5 --- Medium Gravel

8-4 --- 0.3-0.16 5 5 Fine Gravel

4-2 --- 0.16-0.08 9 10 Very Fine Gravel

2.00-1.00 2000-1000 --- 16 18 Very Coarse Sand

1.00-0.50 1000-500 --- 32 35 Coarse Sand

0.50-0.25 500-250 --- 60 60 Medium Sand

0.25-0.125 250-125 --- 115 120 Fine Sand

0.125-0.062 125-62 --- 250 230 Very Fine sand

0.062-0.031 62-31 --- Coarse Silt

0.031-0.016 31-16 --- Medium Silt

0.016-0.008 16-8 --- Fine Silt

0.008-0.004 8-4 --- Very Fine Silt

0.004-0.0020 4-2 --- Coarse Clay

0.0020-0.0010

2-1 --- Medium Clay

0.0010-0.0005

1-0.5 --- Fine Clay

0.0005-0.0002

0.5-0.24 --- Very Fine Clay


January 2018

Case 1 Contraction Scour, from Appendix H, “Evaluating Scour at Bridges”, Hydraulic Engineering Circular No.

18, Federal Highway Administration, Second Edition, April 1993.

Case 1A: Abutments project into channel

Case 1B: Abutments at edge of channel

Case 1C: Abutments set back from channel


January 2018

Cases 2, 3 and 4 Contraction Scour, from Appendix H, “Evaluating Scour at Bridges”, Hydraulic Engineering

Circular No. 18, Federal Highway Administration, Second Edition, April 1993.

Case 2A: River narrows Case 2B: Bridge abutments constrict flow

Case 3: Relief bridge over flood plain Case 4: Relief bridge over secondary stream


January 2018

From “Recording and Coding Guide for the Structure Inventory and Appraisal of the Nation’s Bridges”, Federal

Highway Administration, December 1995.

ITEM 113--SCOUR CRITICAL BRIDGES

Use a single-digit code as indicated below to identify the current status of the bridge regarding its vulnerability to

scour. Scour analyses shall be made by hydraulic/geotechnical/structural engineers. Details on conducting a scour

analysis are included in the FHWA Technical Advisory 5140.23 titled, “Evaluating Scour at Bridges”. Whenever a

rating factor of 4 or below is determined for this item, the rating factor for “Item 60 – Substructure” may need to be

revised to reflect the severity of actual scour and resultant damage to the bridge. A scour critical bridge is one with

abutment or pier foundations which are rated as unstable due to (1) observed scour at the bridge site or (2) a scour

potential as determined from a scour evaluation study.

Code Description

N Bridge not over waterway.

U Bridge with “unknown” foundation that has not been evaluated for scour. Since risk cannot be determined, flag for monitoring during flood events and, if appropriate, closure.

T Bridge over “tidal” waters….

9 Bridge foundations (including piles) on dry land well above floodwater elevations.

8 Bridge foundations determined to be stable for assessed or calculated scour conditions; calculated scour is above top of footing. (Example A)

7 Countermeasures have been installed to correct a previously existing problem with scour. Bridge is no longer scour critical

6 Scour calculation/evaluation has not been made. (Use only to describe cases where bridge has not yet been evaluated for scour potential.)

5 Bridge foundations determined to be stable for calculated scour conditions; scour within limits of footing or piles. (Example B)

4 Bridge foundations determined to be stable for calculated scour conditions; field review indicates action is required to protect exposed foundations from effects of additional erosion and corrosion.

3 Bridge is scour critical; bridge foundations determined to be unstable for calculated scour conditions: --Scour within limits of footing or piles. (Example B) --Scour below spread-footing base or pile tips. (Example C)

2 Bridge is scour critical; field review indicates that extensive scour has occurred at bridge foundations. Immediate action is required to provide scour countermeasures.

1 Bridge is scour critical; field review indicates that failure of piers/abutments is imminent. Bridge is closed to traffic.

0 Bridge is scour critical. Bridge has failed and is closed to traffic.


January 2018

ITEM 113--SCOUR CRITICAL BRIDGES (CONT’D)

Example

Calculated Scour Depth Spread Footing Pile Footing (not founded in rock)

Action Needed

A. Above top of footing

None--indicate rating of 8 for this

item

B. Within limits of

footing or piles

Conduct foundation

structural analysis

C. Below pile tips or spread footing base

Provide for monitoring and

scour countermeasures

as necessary.

Calculated Scour Depth =


January 2018


January 2018

C3.2.2.7.1 Types

C3.2.2.7.2 Design conditions

C3.2.2.7.3 Evaluating existing structures

C3.2.2.7.4 Depth estimates

C3.2.2.7.5 Countermeasures

C3.2.2.7.5.1 Riprap at abutments

C3.2.2.7.5.2 Riprap at piers

C3.2.2.7.5.3 Wing dikes

Determining Wing Dike Lengths

The use of wing dikes (also called spur dikes or guide banks) shall be considered at any bridge site that has

appreciable overbank discharge. Wing dikes help minimize backwater and scour effects. Refer to IDOT’s Office of

Design Standard EW-210 for specific details on slopes, dimensions and other notes. Items that need to be specified

for EW-210 include Length and Station Location.

Generally, the top of dike elevation will be the same as the abutment berm elevation. However, if this berm

elevation is much higher than the Q50 or Q100 elevations, a lower wing dike elevation may be specified.

The following guidelines provide assistance in determining appropriate wing dike lengths. “Long” and “Short” refer

to the longer and shorter wing dikes necessary on skewed bridges as shown onEW-210. If obtaining right of way for

the recommended length is a problem at a bridge site, a shortened wing dike is preferred over no dike.


January 2018

Wing Dike Lengths, in feet (meters)

Bridge Length,

feet (meters)

Bridge Skew

0 deg.

15 deg.

30 deg.

45 deg.

Equal

Long

Short

Long

Short

Long

Short

< 150

(45)

40

(12)

45

(14)

40

(12)

60

(18)

40

(12)

85

(26)

40

(12)

150-180

(45-55)

50

(16)

60

(19)

50

(16)

80

(24)

50

(16)

120

(36)

50

(16)

180-210

(55-65)

65

(20)

75

(23)

65

(20)

100

(30)

65

(20)

150

(45)

65

(20)

210-240

(65-75)

80

(24)

95

(28)

80

(24)

120

(36)

80

(24)

180

(54)

80

(24)

> 240

(75)

95

(28)

105

(32)

95

(28)

140

(42)

95

(28)

205

(63)

95

(28)

C3.2.2.7.6 Coding

C3.3 Highway crossings

C3.3.1 Clearances

C3.3.2 Ditch drainage

C3.4 Railroad crossings

C3.4.1 BNSF and UP overhead structures

C3.4.1.1 Vertical clearance

C3.4.1.2 Horizontal clearance

C3.4.1.3 Piers

C3.4.1.4 Bridge berms

C3.4.1.5 Drainage

C3.4.1.6 Barrier rails and fencing


January 2018

C3.4.2 Non-BNSF and -UP overhead structures

C3.4.2.1 Vertical clearance

C3.4.2.2 Horizontal clearance

C3.4.2.3 Piers

C3.4.2.4 Bridge berms

C3.4.2.5 Drainage

C3.4.2.6 Barrier rails and fencing

C3.4.3 Underpass structures

C3.4.4 Submittals

1 December 2008

In discussions with the BNSF and UP railroads, the office has agreed to provide the new

standard sheet 1067 and the information listed below. This information will be provided

by Preliminary Design Section on the Plan View and Elevation View on the TS & L sheet

of all bridge projects that involve BNSF and UP railroad except the items noted with an

asterisk (*). These items will be provided by the Final Design Sections. Final Design

Sections should review the list to make sure all information is provided.

Plan View

1. Centerline of bridge and/or centerline of project.

2. Track layout and limits of railroad right-of-way with respect to centerline of main

lines.

3. Future tracks, access roadways and existing tracks as main line, siding, spur, etc.

4. Horizontal clearance at right angle from centerline of nearest existing or future

track to the face of obstruction such as substructure above grade.

* 5. Horizontal clearance at right angle from centerline of nearest existing or future

track to the face of nearest foundation below grade.

6. Horizontal spacing at right angle between centerlines of existing and/or future

tracks.

* 7. Limits of shoring and minimum distance at right angle from centerline of nearest

track.

8. All existing facilities and utilities.

9. Existing ground shots and proposed grading.

10. Railroad Milepost and direction of increasing Milepost (Provided by Railroad).

11. Direction of flow for all drainage systems within project limits.

* 12. Limits of barrier rail and fence with respect to centerline of track.

* 13. Location of deck drains (Note drains shall not be located over the railroad right-ofway).

* 14. Total width of superstructure.

15. Width of shoulder and/or sidewalk.

16. North arrow


January 2018

17. Footprint of proposed superstructure and substructure including existing structure if

Applicable

Elevation View

1. Future tracks, access roadways and existing tracks as main line, siding, spur, etc.

2. Point of minimum vertical clearance and distance within the vertical clearance

envelope, measured perpendicular from the centerline of nearest track.

* 3. Limits of shoring and minimum distance at right angle from centerline of nearest

track.

4. Toe of slope and/or limits of retaining wall.

* 5. Limits of barrier rail and fence with respect to centerline of track.

6. Depth of foundation from top of tie / base of rail.

* 7. Top and bottom of pier protection wall elevation relative to top of rail elevation.

8. Controlling dimensions of drainage ditches and/or drainage structures.

9. Top of rail elevations for all tracks.

10. Minimum permanent vertical clearance above the top of high rail to the lowest

point under the bridge.

11. Existing and proposed groundline and roadway profile.

12. Show slope and specify type of slope paving. Toe of slope shall be shown relative

to drainage ditch and top of subgrade.

Note: Items denoted with an asterisk shall be provided by Final Design.

The new 1067 CADD standard shows details of:

1. Railroad General Notes

2. General Shoring Notes

3. General Excavation Zones detail

4. Minimum Construction Clearance Envelope detail

5. Top of Rail Elevations chart.

For additional information, see BNSF Railway – Union Pacific Railroad, Guidelines for

Railroad Grade Separation Projects.

C3.5 Pedestrian and shared use path crossings

C3.6 Superstructures

C3.6.1 Type and span

C3.6.1.1 CCS J-series

C3.6.1.2 Single-span PPCB HSI-series

C3.6.1.3 Two-span BT-series

C3.6.1.4 Three-span PPCB H-series

C3.6.1.5 Three-span RSB-series

https://www.up.com/cs/groups/public/documents/document/pdf_rr_grade_sep_projects.pdf

https://www.up.com/cs/groups/public/documents/document/pdf_rr_grade_sep_projects.pdf


January 2018

C3.6.1.6 PPCB

Preliminary haunch for all Prestressed Beam Bridges

Note: The calculations provide a haunch thickness estimate (X) value, which does not include the nominal haunch thickness.

Longest Span (feet)

Superelevation (feet/feet)

Grade 1 vertical curve [+ increasing, - decreasing] (%)

Grade 2 vertical curve [+ increasing, - decreasing] (%)

Length vertical curve (feet)

Degree of Horizontal Curvature (degree)

Final Beam Camber (feet) - From prestressed concrete beam standards

Dead load deflection - Elastic + 1/2 Plastic (feet) - From prestressed concrete beam standards

Top flange width (feet)

X = Haunch estimate along the centerline of the beam.

~~~~~~~~ ~~~~~~~~

If T * e < 1 then X < 4 in. If T * e > 1 then X < 3 in.

Also check maximum offset for horizontal curve < or = 9 in.

S 111.5ft

e 0.03

G1 1.68

G2 2.10

AG2 G1

100 A 0.038

L 984 ft

Dc 1.75deg

C 0.337ft

D 0.19ft

T 1.667ft

X C D( )S e

2

1

sinDc

2

1

tanDc

2

S

L

2

AL

8 X 0.219ft X 66.894mm

T e 0.6in


January 2018

C3.6.1.7 CWPG

The table below extracted from the AASHTO LRFD Specifications [AASHTO-LRFD 2.5.2.6.3] can be used as a

guide to establish minimum girder depths, when 1/25 of the span is not possible due to vertical clearance or profile

grade issues.

Traditional Minimum Depths for Constant Depth Superstructures

Superstructure

Minimum Depth (Including Deck)

When variable depth members are used, values may be

adjusted to account for changes in relative stiffness of

positive and negative moment sections.

Material Type Simple Spans Continuous Spans

Steel Overall Depth of Composite I-Beam 0.040L 0.032L

Depth of I-Beam Portion of

Composite I-Beam 0.033L 0.027L

Trusses 0.100L 0.100L

From AASHTO LRFD Bridge Design Specifications, 7th Edition, Copyright 2014, by the American Association of State Highway and Transportation Officials, Washington, DC. Used by permission.

C3.6.1.8 Cable/Arch/Truss

C3.6.2 Width

C3.6.2.1 Highway

C3.6.2.2 Sidewalk, separated path, and bicycle lane

When placing sidewalks on bridges, the following policy should be used for determining whether to use raised

sidewalks or sidewalks at grade.

1. Raised sidewalks, which allow water to drain through slots in the separation barrier curb to the bridge gutterline,

shall be used on highway and railroad overpasses.

2. All other situations may use an at grade sidewalk which allows the water to drain over the slab edge.

At grade sidewalks, which drain the water back towards the gutter line, shall not be used. The reason the office

would like to avoid this condition is that it would require the exterior girder to be placed higher than the adjacent

interior girder. In addition, in situations of excessive rainfall the sidewalks may be temporarily flooded because of

water from the roadway. Superelevated bridges may require special considerations. Check with your section leader

in this case.

Regardless of the sidewalk type, the top of the slab where the chain link fence is attached shall be made level and

drip grooves shall be used on the underside of the slab.

C3.6.3 Horizontal curve

C3.6.3.1 Spiral curve

C3.6.4 Alignment and profile grade

For situations where the profile grade line is not at the centerline of approach roadway, elevations for the bridge

deck will be established taking the bridge deck crown into account. The elevations will be noted on the TS&L as


January 2018

“TOP OF BRIDGE DECK AT CENTERLINE ROADWAY IS ‘X’ ABOVE (OR BELOW) THE PROFILE

GRADE TO ACCOUNT FOR DECK CROSS SLOPE AND PARABOLIC CROWN.

For situations where the profile grade line is at the centerline of approach roadway, elevations for the bridge deck

will be established in accordance with BDM 1.7.1.

C3.6.5 Cross slope drainage

C3.6.6 Deck drainage

C3.6.7 Bridge inspection/maintenance accessibility

C3.6.8 Barrier rails


January 2018

Flow Chart for determining Bridge Barrier RailHeight for New Bridges on Interstate and Primary

HighwaysRevised 5 December 2016

Bridge over BNSF or UP RR

Heavy Truck Volume > 7,500Annual Average Daily Truck

Traffic for Design Year

Fracture Critical Elementswithin the zone of intrusion

for truck roll

Fly over Bridge

Unfavorable siteconditions - see guidelines below

Frequent Transitionsbetween Mainline roadway

44" Rail and Bridge Rail

Based on past maintenance experience and current snow removal policies

Is snow pile up a concern?

Have special concerns been raised about headlight glare or ramping due

to snow pile up?

Is plowed snow spilling over roadways, Railroad track or

waterways below, a concern?

Design for TL-4 Barrier Rail (34")

Design for TL-5 Barrier Rail (44")

No

No

No

No

No

No

No

No

No

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Coordinate with Systems Planning

Coordinate With Design

Coordinate With Design

Coordinate with Assistant

District Engineer

Coordinate with Assistant District

Engineer

Coordinate with Assistant

District Engineer

Interstate Bridge

No

Yes


January 2018

Guidelines for unfavorable site conditions (see flow chart above):

• Reduced radius of curvature

• Steep downgrades on curvature

• Variable cross slopes

• Adverse weather conditions

C3.6.9 Staging

C3.7 Substructures

C3.7.1 Skew

C3.7.2 Abutments

C3.7.3 Berms

C3.7.3.1 Slope

C3.7.3.2 Toe offset

C3.7.3.3 Berm slope location table

See also the RBLT example C3.2.7.3.4.


January 2018


January 2018

C3.7.3.4 Recoverable berm location table

See also the BSLT example in C3.2.7.3.3.


January 2018

C3.7.3.5 Slope protection


January 2018

C3.7.3.6 Grading control points


January 2018

C3.7.3.7 Mechanically Stabilized Earth (MSE) Walls adjacent to abutments

C3.7.4 Piers and pier footings

Ref: 2013 AASHTO LRFD Intermediate Revisions


January 2018


January 2018

From AASHTO LRFD Bridge Design Specifications, 6th Edition with Interm Revisions, Copyright 2012-2013, by the American Association of State Highway and Transportation Officials, Washington, DC. Used by permission.


January 2018

C3.7.5 Wing walls


January 2018

C3.8 Cost estimates

C3.9 Type, Size, and Location (TS&L) plans

PRELIMINARY BRIDGE DESIGN TS&L PLAN SHEET(S) LAYOUT GUIDELINES

Refer to the PLAN REVIEW CHECKLIST or PRELIMINARY DESIGN GUIDELINES available on the Bridge Web Site which include required information for the TS&L Plan sheet(s). The following guidelines are intended to provide consistency for placing information when additional plan sheet(s) are needed. The first sheet shall show a typical bridge layout per guidelines and be labeled SITUATION PLAN below the plan view and in the title block. Bridge sites typically have areas of interest such as stream meanders, interchanges, etc. which do not fit on a single Situation Plan sheet. To show these areas, a SITE PLAN sheet shall be created. This second plan sheet shall be labeled as SITE PLAN below the plan layout and the title block shall be labeled as SITUATION PLAN - SITE. The scale of the site plan layout may be changed (labeled with a Scale Legend) to adequately show conditions outside of the proposed structure area. Typically, the SITE PLAN shall be shown on one sheet. The SITE PLAN sheet may also be used to place information when insufficient room remains on the SITUATION PLAN sheet. Any additional sheet(s) showing details or other preliminary information shall be labeled as MISCELLANEOUS DETAILS and the title block(s) should be labeled as SITUATION PLAN - MISC. In general, additional plan sheets shall be created except for relatively small bridges where limited additional information is needed. All items required by the PLAN REVIEW CHECKLIST or PRELIMINARY DESIGN GUIDELINES which are not listed in the mandatory or preferred item guidelines shall be placed at the designer’s discretion. The designer shall follow the guidelines of the mandatory and preferred items listed for both situation plan layout and site plan layout sheets when placing information. Topography is defined as information typically obtained from the project survey such as ground features and utilities, excluding ground shots and contours. The mandatory items listed below shall be shown on the situation plan layout sheet(s). Mandatory Items for the Situation Plan layout sheet(s)

1. Situation Plan o SITUATION PLAN heading under plan view layout o Dimensions of Proposed Structure(s) o North Arrow o Centerline Roadway Alignments and labels o Centerline Stationing labels o Profile Grade Line labels o Existing Structure(s) (A) o Proposed Grading Slope Lines (not proposed contours) (A) o Revetment (A) o Slope Protection Note (A) o Guardrail Indicated o Topography (A)


January 2018

o Minimum Vertical Clearance Location (overhead bridges) o Scale Legend o Horizontal Clearance to Piers (overhead bridges)

2. Longitudinal Section 3. Typical Approach Section 4. Location Data 5. Bench Mark

(A) These items to be edited as required prioritizing clarity of other mandatory items or text. More

comprehensive treatment of these items can be made on the site plan sheet in cases where extensive editing is required on the situation plan layout sheet(s).

The preferred items listed are expected to be shown on the situation plan layout sheet(s) but due to space restrictions may be shown on the site plan layout sheet. Preferred Items for the Situation Plan layout sheet(s) (In order of preference)

1. Proposed Grade 2. Hydraulic Data 3. Traffic Estimate 4. Utilities Legend 5. Spiral Curve Data 6. Horizontal Curve Data 7. Minimum Vertical Clearance note 8. Staging Widths

The mandatory items listed below shall be shown on the site plan layout sheet. Some duplication is necessary for references between the multiple SITUATION PLAN sheets. Mandatory Items for the Site Plan layout sheet

1. Site Plan o SITE PLAN heading under plan view layout o North Arrow o Centerline Roadway Alignments and labels o Centerline Stationing labels o Proposed Structure(s) (B) o Existing Structure(s) (B) o Proposed Grading Slope Lines (not proposed contours) (B) o Revetment (B) o Guardrail Indicated o Topography (B) o Scale Legend o Beginning & End Bridge Stations at Centerline Abutment Bearings

(B) These items should not be edited extensively on the site plan layout sheet and a more

comprehensive treatment of these items should be shown on this sheet where extensive editing may have been necessary on the situation plan layout sheet(s).

The preferred items listed are expected to be shown on the site plan layout sheet but due to space restrictions may be shown on the situation plan layout sheet(s). Preferred Items for the Site Plan layout sheet

1. Berm Slope Location Table & Associated Point I.D. Labels (Show together on the sheet) 2. Revetment Limits & Typical Section Details 3. Survey Ground Shots or Contours of existing ground supplemented with Ground Shots (not

proposed contours)


January 2018


January 2018

C3.10 Permits and approvals

C3.10.1 Waterway

Department of Natural Resources List of Meandered Streams 22 December 2006

Iowa Department of Natural Resources Sovereign Lands Construction Permits are required for work on or

over meandered streams. (This is a different permit than a Floodplain Development Permit.) The term

“meandered stream” for this permit is a legal description where the State of Iowa owns the stream bed and

banks of certain reaches of rivers. A meandered stream is one which at the time of the original government

survey was so surveyed as to mark, plat and compute acreage of adjacent fractional sections. DNR is

responsible for this state-owned land and therefore issues a Construction Permit. The following is a list of

the descriptions of the limits of these rivers in the state of Iowa.

1. Des Moines River. From Mississippi River to the junction of the east and west branches. The west

branch to west line T95N, R32W, Palo Alto County, due south of Emmetsburg. The east branch to

north line T95N, R29W, Kossuth County, near the north edge of Algona.

2. Iowa River. From Mississippi River to west line T81N, R11W, Iowa County, due north of Ladora.

3. Cedar River. From Iowa River to west line T89N, R13W, Black Hawk County, at the east edge of

Cedar Falls.

4. Raccoon River. From Des Moines River to west line of Polk County.

5. Wapsipinicon River. From Mississippi River to west line T86N, R6W, Linn County northwest of

Central City.

6. Maquoketa River. From Mississippi River to west line T84N, R3E Jackson County, due north of

Maquoketa.

7. Skunk River. From Mississippi River to north line of Jefferson County, at the southwest edge of

Coppock.

8. Turkey River. From Mississippi River to west line T95N, R7W, Fayette County, northwest of

Clermont.

9. Nishnabotna River. From Missouri River to north line T67N, R42W, Fremont County, northeast

of Hamburg.

10. Upper Iowa River. From Mississippi River to west line Section 28, T100N, R4W, Allamakee

County, about two and one-half miles upstream from its mouth.

11. Little Maquoketa River. From Mississippi River to west line Section 35, T90N, R2E, Dubuque

County, about one mile upstream from its mouth.

12. Mississippi River, Missouri River, Big Sioux River.


January 2018

C3.10.2 Railroad

C3.10.3 Highway

C3.11 Forms

Examples of forms to follow:


January 2018


January 2018

C3.12 Noise walls

Excerpts from AASHTO LRFD Bridge Design Specifications,7th Edition, Section 15: Design of Sound Barriers,

Copyright 2014, by the American Association of State Highway and Transportation Officials, Washington, DC.

Used by permission:


January 2018


January 2018

C3.13 Submittals


January 2018

C3.14 Zone of Intrusion

Figures adapted from AASHTO Roadside Design Guide,4th Edition.

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